In electrostatography, an image charge pattern (also referred to as an electrostatic latent image) is formed on an imaging element and is then developed by treatment with an electrostatographic developer containing toner particles (collectively "toner") that are attracted to the charge pattern. The resulting toner image can be transferred to a receiver such as a sheet of paper, and fused (or fixed) to the receiver in a fuser system.
The fusing system typically applies heat and pressure to the toner bearing receiver by passage through a nip defined by a pair of opposing fuser members, such as a pair of rollers maintained in pressure contact (one or both being heated, such as a combination of a fuser roller and a pressure roller), a flat or curved plate member and a roller in pressure contact, or a belt in pressure contact with a roller. Heat may be applied by heating one or both of the fuser members. Heat is necessary to make the toner particles tacky and flowable into the fibers or pores of the receiver, providing firm bonding thereto.
Members of a useful fuser system generally are referred to as "fuser members", and can include one or more fuser rollers, and one or more pressure rollers. The fuser roller generally contacts the toner image while the pressure roller (or backup roller) contacts the opposite surface of the receiver.
Alternatively, the toner image on the imaging element can be transferred from the imaging element to an intermediate transfer member (ITM), and then transferred from the ITM to a receiver and fixed in the fuser system. Transferring toner images to the ITM is particularly desirable when forming multi-color images, because the individual color separations in the image can be developed separately on the imaging member, transferred separately from the imaging element to the ITM so that the individual color separations are accumulated in registration on the ITM, and then the accumulated color separations are transferred in one step from the ITM to the receiver.
It is known to use fuser members comprising metal supports having one or more elastomeric layers disposed thereon. The elastomeric layers provide the proper nip width, thermal and electrical properties, and release characteristics for both fusing and image transfer. However, obtaining strong adhesion between the elastomeric materials and the metal supports is a continuing challenge in the industry. By improving the adhesion between the elastomeric layer and the metal, the useful life of the fuser members can be extended.
Various means have been tried to provide the desired adhesion between elastomeric layers and the metal supports, including mechanical and chemical treatments, such as chemical etching, alkaline treatment and acid anodizing.
Another way to address this problem is to use primer layers between elastomeric layers and metal supports of fuser members, as described for example, in U.S. Pat. No. 4,196,256 (Eddy et al). Further, U.S. Pat. No. 5,474,821 (Kass) discloses the use of chromate conversion to improve the adhesion of silicone rubber to an aluminum support in the production of a fuser member.
However, methods of applying primers and chromate conversion suffer from the drawbacks that they are imprecise and provide an uneven application of the materials to the surface of the support, resulting in uneven adhesion of the elastomeric materials to the supports, and shorter useful life for fuser members. Additionally, these methods require increased manufacturing times, to allow the primers and conversion coatings to dry. Primers and the solvents from which they are coated pose an environmental concern, both to the manufacturing workers as well as to the general public. All of these disadvantages have prompted workers in the art to explore novel solutions to the adhesion problem.
Corona discharge is well known as a treatment for improving the adhesion of various materials to resins, composites, and metals of various shapes. Particularly, it is known for improving the adhesion of thermoplastic resins to various coatings (see U.S. Pat. No. 5,466,423 of Brinton et al). Vulcanized resins of various shapes (including golf balls) have been treated with corona discharge to change surface characteristics as described in U.S. Pat. No. 5,466,424 (Kusano et al).
U.S. Pat. No. 4,988,536 (Van Dongen et al) describes the use of corona discharge treatment of metals having a lightly oiled surface to improve the adhesion thereto of lacquers.
U.S. Pat. No. 5,547,759 (Chen et al) describes the use of various treatments including primer layers and corona discharge to adhere one elastomeric layer to another on a fuser member.
It would be desirable to have a method of providing improved adhesion between an elastomeric layer and the bare metal support of electrostatographic members, such as fuser members, without the use of primers or other treatments of known methods that cause problems.